For the growth of gallium nitride-based semiconductor layer sequences, it is possible, for example, to use a silicon substrate, as a growth substrate. In that case, the different coefficients of thermal expansion of silicon (2.6*10−6/K at room temperature) and GaN (4.2*10−6/K at room temperature) during and after growth can lead to flexure of the semiconductor layer sequence and the growth substrate. The consequences are an inhomogeneous crystal quality of the semiconductor layer sequence and an increased risk of cracking in the semiconductor layer sequence. The same problem can occur during the rebonding of the semiconductor layer sequence onto a replacement substrate composed of silicon.
Measures for avoiding these problems extend to the use of buffer structures which, at growth temperature, enable a compressively strained growth of the semiconductor layer sequence, such that, upon cooling to room temperature, as a result of the different coefficients of thermal expansion, the compressive strain can be compensated for and only a low tensile strain of the semiconductor layer sequence is established. The buffer structure can be formed from a layer sequence of AlN/AlGaN/GaN, for example. However, disadvantages of a semiconductor layer sequence with a buffer structure of this type are, inter alia, the reduced vertical and lateral current conductivity in the completed semiconductor chip.
Therefore, it could be helpful to provide a composite substrate which enables a semiconductor chip having improved electrical properties. Furthermore, it could be helpful to provide an optoelectronic semiconductor chip having improved electrical properties.